Diabetic foot infection and osteomyelitis. Are deep-tissue cultures necessary?

Diabetic foot infections (DFIs) are common and difficult to treat. The objective of this study was to compare swab and tissue cultures as indicators of appropriate treatment of DFIs.

This is a prospective study conducted during a 4-year period. All patients with DFIs and/or diabetic foot osteomyelitis (DFO) admitted to the University Hospital of Heraklion, Greece, were included. Clinical data were collected, while cultures taken with swabs and/or tissue biopsies were used as indicators of the microbiological cause and the appropriate treatment.

In total, 83 individuals (62.7% males) with mean age of 72 years, were enrolled. Coexisting osteomyelitis was present in 18.1%. From tissue and pus cultures, 131 and 176 pathogens, respectively, were isolated. Gram-positive aerobes were the most common microorganisms, followed by Gram-negatives. Infection was polymicrobial in 40 (70.2%) out of 57 patients with tissue culture and in 54 (75.0%) out of 72 with pus culture. Microbiological results from tissue cultures were compatible with those from pus at a rate of 80%, while in cases of osteomyelitis concordance reached 100%. Multidrug-resistant organisms (MDROs) were isolated from 32 (24.4%) tissue and 44 (25%) pus cultures (p=0.910). Initial empirical antimicrobial treatment was considered inappropriate in 44.6% of cases.

A high concordance between easily taken swab cultures and those taken by biopsy was noted, especially in DFO. This was helpful for early change to appropriate treatment in cases where MDROs were isolated and empirical treatment was inappropriate. Further research is needed to confirm this observation in clinical practice.